Integrated circuits (ICs) are typically composed of several layers of conducting, insulating and other components that are structured in a horizontal dimension by fabrication processes.
Shorts and Opens are two categories of random yield defects that occur during the fabrication process. EMCA (Extra Material Critical Area) is a measure of an integrated circuit layout geometry that defines the susceptibility of the device to defects that unintentionally make an electrically conductive connection between conductive regions of the circuits (“Shorts”). MMCA (Missing Material Critical Area) is a measure of an integrated circuit layout geometry that defines the susceptibility of the device to defects that unintentionally interrupt an electrical connection between conductive regions of the circuit (“Opens”). “Extra material” defects are defects which cause shorts between different conducting regions and “missing material” defects are defects which cause open circuits in a conducting region.
Yield losses may also be caused by insufficient, excessive, or inhomogeneous material density. Fabrication of ICs typically requires that material density—that is, the percentage of conductive material in a conductor layer, averaged across spatial regions of specified size—lies within specified upper and lower limits and does not change rapidly between adjacent such regions. Fabrication processes can typically be simplified, executed in a more robust manner and achieve higher yield if spatial variations in material density can be reduced by appropriate layout.
It is known in the art to modify the routing layout and geometry of conductors, vias, contacts and other components in order to reduce yield defects.